Webcrypto API - How to provide array buffers ( signature and public key ) as strings?

Question

I'm using the Webcrypto API to sign data and now have the public key and signature both of type ArrayBuffer. Both information should be stored into separate files, so

• the public key should be stored as a string into a "public_key" file
• the signature should be stored as a string into a "signature" file

I'm new to this and don't know the "easiest" file formats so other languages/packages ( e.g. Java backends ) can deal with the files.

For the public key the SPKI format as a PEM string looks fine? But I don't know an approach for the signature. I started with the following

( Playground link )

const generateKeyPair = async function() {
    return crypto.subtle.generateKey(
        {
            name: "ECDSA",
            namedCurve: "P-384",
        },
        true,
        ["sign", "verify"]
    );
};

const sign = async function(privateKey: CryptoKey, buffer: BufferSource) {
    return crypto.subtle.sign({
      name: privateKey.algorithm.name,
      hash: 'SHA-512'
    }, privateKey, buffer);
};

const exportKeyAsSPKI = async function(cryptoKey: CryptoKey) {
    return crypto.subtle.exportKey("spki", cryptoKey)
};

const spkiToPEM = function(buffer: ArrayBuffer) {
    const asString = String.fromCharCode.apply(null, new Uint8Array(buffer));
    const asBase64 = btoa(asString);
    
    return `-----BEGIN PUBLIC KEY-----\n${asBase64}\n-----END PUBLIC KEY-----`;
};

(async () => {
    // Generate keys 
    
    const { privateKey, publicKey } = await generateKeyPair();

    // Sign data

    const data = { foo: 'bar' };
    const stringifiedData = JSON.stringify(data);
    const buffer = new TextEncoder().encode(stringifiedData);
    
    const signature = await sign(privateKey, buffer);

    // Convert public key to string to store into file

    const publicKeyAsSPKIFormat = await exportKeyAsSPKI(publicKey);
    const pemEncodedKey = spkiToPEM(publicKeyAsSPKIFormat);

    // Convert signature to string to store into file

    // ... TODO ...

    // DONE

    console.log("Public key:");
    console.log(pemEncodedKey);

    console.log("Signature:");
    console.log("todo...");
})();

What is the approach for the signature? Are there any better approaches for the public key?